In order to create various light effects and mood lighting in connection with concerts, live shows, TV shows, sport events or as a part of an architectural installation light fixtures creating various effects are getting more and more use in the entertainment industry. Typically, entertainment light fixtures create a light beam having a beam width and a divergence and can for instance be wash/flood fixtures that create a relatively wide light beam with a broad light distribution, profile fixtures adapted to project images onto a target surface, or hybrid/beam fixtures capable of creating sharp light beam for mid-air light effects.
Light emitting diodes (LED) are becoming more and more used in connection with lighting applications due to their relatively high efficiency, low energy consumption, long lifetime, and/or capability of electronic dimming. Presently, LEDs are used in both wash/flood, projecting and hybrid light fixtures.
In general, it is desired to have a multi-colored LED lighting product with a high lumen output and also a high Color Rendering Index (CRI). However, this is hard to achieve when using LEDs in a light fixture where the light is coupled through an optical gate. Due to Etendue limitations, it is not possible to combine light from an unlimited amount of light sources into a light beam which is coupled through an optical gate. This is the case in connection with projecting light fixtures where an image creating objects (GOBO) is positioned in or close to the optical gate and where an optical projecting system collects the light from the optical gate and is adapted to image the optical gate (and thus also the image creating object) at a target surface. The light beam is very narrow when it passes the optical gate and such projecting systems are thus limited by Etendue. The Etendue (i.e., as defined by the following equation, E=A*Ω) at the gate through which light is emitted has a limited opening area A and the imaging optics only collect light from a limited solid angle Ω. For light sources, the Etendue can be calculated in the same way, where A is the radiating area, and Ω is the solid angle it radiates light into.
In addition to high lumen output and high CRI, it is also desired to have very compact illumination devices, which is difficult to achieve when more light sources are being integrated into the same illumination device.
In projecting light fixtures, the light is generally collected into an optical gate where the image is generated, and an imaging optical system projects the gate onto a target surface. WO0198706, U.S. Pat. No. 6,227,669 and U.S. Pat. No. 6,402,347 disclose lighting systems comprising a number of LEDs arranged in a plane array where a converging lens is positioned in front of the LED in order to focus the light, for instance, to illuminate a predetermined area/gate or for coupling the light from the diodes into an optical fiber.
U.S. Pat. No. 5,309,277, U.S. Pat. No. 6,227,669, WO0198706, JP2006269182 A2, EP1710493 A2, and U.S. Pat. No. 6,443,594 disclose lighting systems where the light from a number of LEDs is directed towards a common focal point or focusing area, for instance, by tilting the LEDs in relation to the optical axis (JP2006269182 A2, WO0198706, and U.S. Pat. No. 5,309,277) or by using individually refracting means positioned in front of each LED (U.S. Pat. No. 6,443,594, U.S. Pat. No. 7,226,185B, and EP1710493).
WO06023180 discloses a projecting system comprising a LED array with a multiple number of LEDs where the light from the LEDs is directed towards a target area. The LEDs may be mounted to a surface of a curved base.
The prior art fixtures try to increase the lumen output by adding as many light sources as possible. The consequence is, however, that the efficiency with regard to power consumption versus light output is very low, as it is fundamentally only possible to effectively utilize light sources of same or less Etendue as the imaging optics in this kind of optical system. If the source Etendue is a close match to the Etendue of the imaging system, there are no gains in using multiple sources in order to increase the light output (intensity/lumen) as the Etendue of the light sources then will be larger than the Etendue of the imaging system and the imaging system is thus not capable of collecting the light.
WO11076213 and WO11076219 disclose an illumination device comprising a light source module generation light, an aperture delimiting the optical gate and a projecting system adapted to image the optical gate at a target surface. The light source module comprises a number of light sources and a number of light collecting means. The light collecting means comprise a central lens aligned along and a peripheral lens at least partially surrounding the central lens. The central lens collects and converts a first part of the light from the light source and images the light source between the aperture the projecting system. The peripheral lens part collects and converts a second part of the light from the light source and is adapted to concentrate the second part of the light at the aperture. The light source module comprises a cooling module comprising a number of interconnected plane mounting surfaces angled in relation to each other and where the light sources is arranged on the plane mounting surfaces. The cooling module comprises a first side comprising the mounting surfaces and a second side comprising a number of cooling fins defining a number of radial air channels.
Even though the illumination device as disclosed in WO11076213 and WO11076219 is very effective, it has some disadvantages as it is relatively expensive to manufacture as the LEDs and TIR lenses needs to be arranged individually.
EP2881650, EP2881651, EP2881652, and EP2881653 disclose illumination devices comprising a plurality of light sources emitting light, an optical gate; a light collector arranged between the light sources and optical gate and an optical projecting system adapted to image the optical gate at a distance along the optical axis. The light collector is adapted to collect light from a plurality of light sources and the light collector comprises a plurality of lenslets collecting light from the light sources and converting the light into a plurality of light beams propagating along an optical axis. The lenslets can be arranged in a dense pattern, where a plurality of outermost adjacent lenslets is located along an outer circular boundary having the same radial distance to a center of the light collector. The dense pattern can been obtained by optimizing a packaging density defined by a ratio of a sum of areas of circular cross sections of the lenslets and an area of the outer circular boundary. The dense pattern comprises adjacent lenslets, where the lenslets of at least some of the pairs of the adjacent lenslets have different optical power and wherein the exit surfaces of the pairs of the adjacent lenslets having different optical power meet along a boundary. The axial distances between the lenslets and light sources along the optical axis for adjacent lenslets are different for at least some of the adjacent lenslets. There is a desire to increase the light output of a illumination devices disclosed by EP2881650, EP2881651, EP2881652, and EP2881653. Additionally some phosphor based LED's have an uneven color distribution across the emitting surface, mainly due to variation in phosphor thickness and as a consequence the illumination at the optical gate provided be the systems disclosed by EP2881650, EP2881651, EP2881652, and EP2881653 may vary from protest to product.